Haze-free transparent laminate having a plasticized polyvinyl acetal sheet

Abstract

A method for overcoming laminate failure in laminated windows containing adjacent layers of polycarbonate and plasticized polyvinyl acetal is disclosed. The method involves applying a protective adhesive means such as a film of a polyurethane or an epoxy resin to a major surface of at least one of the sheets, assembling the sheets with said film on an interfacial surface of the assembly, and laminating the assembly at high temperature and pressure. Also disclosed are various laminate configurations containing a plasticized polyvinyl acetal-polycarbonate interfacial surface treated according to the present invention. Such laminates are useful as substantially haze-free, transparent articles, such as windows for aircraft.

I claim: 
     
       1. A substantially haze-free transparent laminate comprising a sheet of polycarbonate, a sheet of polyvinyl acetal plasticized with a plasticizer that produces haze in said polycarbonate when said plasticized polyvinyl acetal contacts said polycarbonate and a layer of polyurethane or an epoxy resin interposed between the interfacial surfaces of said sheet of polycarbonate and said sheet of polyvinyl acetal so plasticized for protecting said polycarbonate sheet from haze produced by contact with said plasticized sheet and for bonding said sheets together. 
     
     
       2. The laminate of claim 1 in which the polyvinyl acetal is polyvinyl butyral. 
     
     
       3. The laminate of claim 1 in which the polyurethane is a polycondensate of an organic diisocyanate, a diol selected from the class consisting of polyester diols and polyether diols, and a curing agent containing at least two active hydrogens. 
     
     
       4. The laminate of claim 1 in which the epoxy resin is a self-condensed epoxy resin of epichlorohydrin and 2,2-bis(4-hydroxyphenyl) propane. 
     
     
       5. The laminate of claim 1 in which said layer of polyurethane or epoxy resin has a thickness of 0.01 to 50 mils. 
     
     
       6. The laminate of claim 1 in which the bond strength between said polycarbonate sheet and said polyvinyl acetate sheet is at least 20 pounds per lineal inch as measured by NASA Tech Brief 65-10173. 
     
     
       7. The laminate of claim 2 said polyvinyl butyral is plasticized with triethylene glycol di-(2-ethyl butyrate).